The primary objective of this proposal is to study the different lymphocyte populations in the peripheral blood of persons who were exposed to x-ray treatment to their thymus gland during their infancy or early childhood. Also, we will determine the different lymphocyte popultion of the periphral blood of patients with cancer, before and after they have been treated with radiation. The response of the lymphocytes to different mitogens will also be determined in these patients and their chromosomal patterns determined. If any abnormal chromosomes are found, more detailed chromosomal studies, using the newer techniques, will be done.